High-profile climate activists are already branding Cop26 a failure but other voices are warning their message of doom could be as bad as denying climate change altogether.

The first week of the climate summit has brought some major commitments but critics say they are just more hot air.

Here is a guide to what big personalities in the climate fight are saying so far.

– Greta Thunberg

Greta Thunberg told protesters gathered in Glasgow on Friday: “Many are starting to ask themselves, what will it take for the people in power to wake up?

“But let’s be clear, they are already awake. They know exactly what they are doing – they know exactly what priceless values they are sacrificing to maintain business as usual.”

Thunberg added: “The leaders are not doing nothing, they are actively creating loopholes and shaping frameworks to benefit themselves and to continue profiting from this destructive system.

“This is an active choice by the leaders to continue to let the exploitation of people in nature and the destruction of present and future living conditions to take place.”

She described the summit as “a beautiful PR event” and a “greenwash festival” orchestrated by wealthy countries in the global north.

-John Kerry

Thunberg’s words were in stark contrast to the optimism of John Kerry at a business dinner on Thursday evening, where he said that according to the International Energy Agency pledges made so far at the conference would limit warming to 1.8C.

Ahead of the Cop, analysis showed humanity was on course for 2.7C.

Mr Kerry also revealed the target of 100 billion dollars (£74.1 billion) in climate finance pledged by wealthy nations to developing countries would be met by 2022, a year earlier than previously predicted.

The US climate envoy told delegates: “I believe that we are going to be able to raise the ambition beyond anything we imagined – already we have finance that is very significant.”

Professor Michael E Mann

Pioneering climate scientist Professor Michael E Mann, one of the people behind the famous hockey stick graph of global warming, has criticised some activists for their outlook on social media.

In a tweet on Friday, he said: “Beware of the slippery slope from cynicism to nihilism. It leads to the same place as denialism: inaction.

“Which is precisely what polluters and those doing their bidding want.”

In an earlier post he said: “Cop26 has barely started. Activists declaring it dead on arrival makes fossil fuel executives jump for joy.

“They want to undermine and discredit the very notion of multilateral climate action.”

Vanessa Nakate

Ugandan activist Vanessa Nakate struck a more optimistic note at the Fridays for Future protest.

Describing what the world could look like if humans tackle climate change, she said: “The climate crisis is here now.

“But the dry land can be glad again, the farms can blossom again, the animals can rejoice because there is water to drink, there is a loud singing in once parched lands.

“The pain and suffering is gone, there is a celebration of the people because the disasters are gone.”

She continued: “We won’t have to fight for limited resources, because there will be enough for everyone.”

Professor Rebecca Willis, a specialist in environmental policy at the University of Lancaster, believes a little hope can be a powerful thing.

She told the PA news agency: “It is really important not to terrify ourselves because the danger is that leads to absolute fatalism.”

Prof Willis added: “1.5C is better than the 1.6C, which in turn is better than 1.7C, the more greenhouse gases we can keep out of the atmosphere, the better.”